On Sat, May 21, 2016 at 1:40 PM, Pedro Giffuni <p...@freebsd.org> wrote: > > > On 05/21/16 14:05, Conrad Meyer wrote: >> Won't this still return a negative integer in many cases? >> >> random(9) returns u_long, whereas this rand() routine returns 'int'. >> >> Even on architectures where long is the same size as ordinary >> integers, the range of possible results of the 'random() / 2 + 1' >> expression, before implicit cast to signed, is [1, 2^31] (inclusive). > > > According to: > sys/libkern/random.c > > The result is uniform on [0, 2^31 - 1].
Ah, I missed that. Sorry! In that case, I'm not sure why this is needed — the result fits in a non-negative 2's complement signed integer. >> 2^31 is not representable by typical signed 32-bit integers, so this >> will wrap to INT_MIN. Also, I'm not sure why zero is excluded from >> the range. >> > > It is not a good reason but the zero is sometimes inconvenient: if > the value is going to be used as a multiplier in some calculation > it will basically kill the random component. Sure, but anyone using a random number as a multiplier must consider the range of the random function. They should handle rand() == 0 (perhaps by this '/ 2 + 1' construct). I don't think that is the responsibility of a rand() function. Best, Conrad _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
